The present invention relates to a method of performing facsimile transmissions, involving the sending of one or more non-standard tones from the called facsimile machine to the calling facsimile machine at the beginning of the call, and to facsimile machines implementing this method.
Facsimile transmission methods have been standardized by the Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T) in Recommendation T.30, entitled Procedures for Document Facsimile Transmission in the General Switched Telephone Network. In these methods, the transmission of facsimile image data is preceded by a handshaking sequence in which the called facsimile machine informs the calling facsimile machine of the capabilities supported by the called facsimile machine, and the calling facsimile machine selects the capabilities to be used during the transmission. These capabilities may include both standard capabilities described in Recommendation T.30, and non-standard capabilities provided by various manufacturers. The handshaking sequence may also include such features as a password check.
Because of the many non-standard capabilities provided by recent facsimile machines, the handshaking procedure can take considerable time. The handshaking time may exceed the facsimile-page transmission time, for example. In this case every facsimile transmission begins with a noticeable delay that the user would prefer to avoid. Some recent facsimile machines, which incorporate modulator-demodulator facilities complying with ITU-T Recommendation V.34, shorten the handshaking time by transmitting the information about machine capabilities at a high-speed data rate, but these V.34-capable facsimile machines require additional handshaking to establish V.34 communication parameters, so there is still a significant delay at the beginning of every facsimile transmission.
A known method of avoiding such delays equips a facsimile machine with a memory for storing information about the capabilities of distant facsimile machines to which speed dialing numbers are assigned. The user enters this information when assigning the speed dialing numbers. When calling a distant facsimile machine known to have certain capabilities, the user's facsimile machine sends a tone informing the distant facsimile machine that its capabilities are known and information about them does not have to be sent.
A disadvantage of this method is that it is inconvenient for the user to have to enter extra information when assigning speed dialing numbers. In many cases the necessary information will not even be available to the user. A further disadvantage that the user may enter the information incorrectly, creating communication problems later.
Another type of delay that the user would like to avoid occurs when the facsimile transmission cannot be completed for some reason, such as an invalid password, but this does not become known until midway through the handshaking sequence.